it is easy enough to recognise a person at a distance as someone you know or the symbols on there shield or tunic. this was the whole purpose of heladry and coast of arms after all to be able to know your friends and enemies on the field of battle.
OK this makes three assumptions I can't agree with
1. Who says wearing a shield or tunic with symbols to be able to identify someone with is comon practice in PS? This wasn't even that comon as is said here in medevil times.
Just think of movies like Braveheart and Arthur. Did you see the scots wearing uniforms? Wearing shield to show what lord they served? Would you be able to tell from what clan wich scot is? I would think not. Seen the Saksen horde? Do you see any identifying ffeatures there?
And these are movies that make sure there are differences. Movies where the armor will shine and be placed right in view so you know what side you are looking at.
2. As far as I know heraldy is a knight thing and most of the participant in a battle wouldn't be knights. There are pikeman and crossbowmen and swordsmen. Even if both sides would be using them only the leaders would have such a shield most likely. And even if they had each knight would have their own symbols. With 300 knights on each side would you know all your oponents symbol by heart?
3. As far as I know heraldy was used a symbol for the family plus personal symbols. Simply to show what you stood for and to make identifying easy in a mostly illiterate society. That these sybols then would be set on shields somtimes as a show of pride hardly makes that they made the symbols to be recognized on the battlefield.